The term aṣ-ṣaḥābah (Arabic: الصحابة‎ meaning "the companions", from the verb صَحِبَ meaning "accompany", "keep company with", "associate with") refers to the companions, disciples, scribes and family of the Islamic prophetMuhammad. This form is definite plural; the indefinite singular is masculine ṣaḥābī, feminine ṣaḥābīyah.

Later scholars accepted their testimony of the words and deeds of Muhammad, the occasions on which the Quran was revealed and various important matters of Islamic history and practice. The testimony of the companions, as it was passed down through chains of trusted narrators (isnads), was the basis of the developing Islamic tradition. From the traditions (hadith) of the life of Muhammad and his companions are drawn the Muslim way of life (sunnah), the code of conduct (sharia) it requires and the jurisprudence (fiqh) by which Muslim communities should be regulated. The two largest Islamic denominations, the Sunni and Shia, take different approaches in weighing the value of the companions' testimony, have different hadith collections and, as a result, have different constructed views about the Sahabah.

The most widespread definition of a companion is someone who saw Muhammad, believed in him and died as a Muslim. Anyone who died after rejecting Islam and becoming an apostate is not considered as a companion. Those who saw him but held off believing in him until after his passing are not considered Sahaba but Tabi`in. Shia Muslims make no distinction between these as regards their trustworthiness[1]

However, scholars like Javed Ahmad Ghamidi and Amin Ahsan Islahi state that not every individual who met or had accidentally seen Muhammad can be considered as a Companion. In their view, the Quran has outlined a high level of faith as one of the distinctive qualities of the Sahabah. Hence, they admit to this list only those individuals who had substantial contact with Muhammad, lived with him, and took part in his campaigns and efforts at proselytizing.[2] This view has implications in Islamic law since narrations of Muhammad transmitted through the Sahabah acquire a greater status of authenticity.

Lists of prominent companions usually run to 50 or 60 names, being the people most closely associated with Muhammad. However, there were clearly many others who had some contact with Muhammad, and their names and biographies were recorded in religious reference texts such as Ibn Sa'd al-Baghdadi's (Muḥammad ibn Sa'd) early Kitāb at-Tabāqat al-Kabīr (The book of The Major Classes). The book entitled Istî’âb fî ma’rifat-il-Ashâb by Hafidh Yusuf bin Muhammad bin Qurtubi (death 1071) consists of 2,770 biographies of male and 381 biographies of female Sahabah. According to an observation in the book entitled Mawâhib-i-ladunniyya, an untold number of persons had already converted to Islam by the time Muhammad died. There were 10,000 by the time Mecca was conquered and 70,000 during the Battle of Tabouk in 630. Some Muslims assert that they were more than 200,000 in number: it is believed that 124,000 witnessed the Farewell Sermon Muhammad delivered after making his last pilgrimage (hajj) to Mecca.

Two important groups among the companions are called the Muhajirun or "exiles" - those who had faith in Muhammad when he began to preach in Mecca who fled with him when he was persecuted there - and the Ansar - people of Medina who welcomed Muhammad and his companions and stood as their protectors. Chapter (sura) 9 of the Quran ("Repentance" (At-Tawba)), verse (ayah) 100 says;

The vanguard (of Islam)- the first of those who forsook (their homes) and of those who gave them aid, and (also) those who follow them in (all) good deeds,- well-pleased is Allah with them, as are they with Him: for them hath He prepared gardens under which rivers flow, to dwell therein for ever: that is the supreme felicity.

Allah turned with favour to the Prophet, the Muhajirs, and the Ansar,- who followed him in a time of distress, after that the hearts of a part of them had nearly swerved (from duty); but He turned to them (also): for He is unto them Most Kind, Most Merciful.

The people who were Muslims at the time of Badr. They are further classified into two:

Muhajreen (immigrants - from Mecca)

Ansar (helpers - inhabitants of Medina (previously known as Yathrib)) They are ideals for the other Muslims because "well-pleased is Allah with them" (Arabic: رضي الله عنه‎ raḍiyu l-Lāhu ‘anhu)[3]

Those who believed, and adopted exile, and fought for the Faith, with their property and their persons, in the cause of Allah, as well as those who gave (them) asylum and aid,- these are (all) friends and protectors, one of another.

According to Sunni scholars, Muslims of the past should be considered companions if they had any contact with Muhammad, and they were not liars or opposed to him and his teachings. If they saw him, heard him, or were in his presence even briefly, they are companions. All companions are assumed to be just (udul) unless they are proven otherwise; that is, Sunni scholars do not believe that companions would lie or fabricate hadith unless they are proven liars, untrustworthy or opposed to Islam.[10] "Whom God is pleased with" (Arabic: رضي الله عنه‎ raḍiyu l-Lāhu ‘anhu) is usually mentioned by Sunnis after the names of the Sahaba.

Some Quranic references are important to Sunni Muslim views of the reverence due to all companions;[11][12][13][14][15][16]

...and He has restrained the hands of men from you; that it may be a Sign for the Believers,...

Those who believe, and adopt exile, and fight for the Faith, in the cause of Allah as well as those who give (them) asylum and aid,- these are (all) in very truth the Believers: for them is the forgiveness of sins and a provision most generous.
And those who accept Faith subsequently, and adopt exile, and fight for the Faith in your company,- they are of you.

In another place the Quran distinguishes between the community in honour:

Not equal among you are those who spent (freely) and fought, before the Victory, (with those who did so later). Those are higher in rank than those who spent (freely) and fought afterwards. But to all has Allah promised a goodly (reward).

It sometimes admonishes them, as when Aisha, daughter of the first Sunni caliphAbu Bakr and the wife of Muhammad, was accused of infidelity:

Why did not the believers - men and women - when ye heard of the affair,- put the best construction on it in their own minds and say, "This (charge) is an obvious lie"?
...Behold, ye received it on your tongues, and said out of your mouths things of which ye had no knowledge; and ye thought it to be a light matter,...

Certain of the desert Arabs round about you are hypocrites, as well as (desert Arabs) among the Medina folk: they are obstinate in hypocrisy: thou knowest them not: We know them: twice shall We punish them: and in addition shall they be sent to a grievous penalty.

In view of such admonitions Shias have different views on each Sahabi, depending on what he or she accomplished. They do not accept that the testimony of nearly all Sahabah is an authenticated part of the chain of narrators in a hadith and that not all the Sahaba were righteous just because they saw or were with Muhammad. Shias further argue that the righteousness of Sahabah can be assessed by their loyalty towards Muhammad's family after his death and they accept hadith from the Imams of the Ahl al-Bayt, believing them to be cleansed from sin through their interpretation of the Quran, surah 33 (Al-Ahzab), verse 33[21] and the hadith of the Cloak.

The Prophet is closer to the Believers than their own selves, and his wives are their mothers. Blood-relations among each other have closer personal ties, in the Decree of Allah. Than (the Brotherhood of) Believers and Muhajirs: nevertheless do ye what is just to your closest friends: such is the writing in the Decree (of Allah).

Shias support their argument that one must discriminate between the virtues of the companions by verses relating to Muhammad's wives:

O Consorts of the Prophet! If any of you were guilty of evident unseemly conduct, the Punishment would be doubled to her, and that is easy for Allah.
But any of you that is devout in the service of Allah and His Messenger, and works righteousness,- to her shall We grant her reward twice: and We have prepared for her a generous Sustenance.

Because the hadith were not properly written down until many years after the death of Muhammad, although there were many individual written copies, the isnads, or chains of transmission, always have several links. The first link is preferably a companion, who had direct contact with Muhammad. The companion then related the tradition to a Tabi‘un, the companion of the companion. Tabi‘un had no direct contact with Muhammad, but did have direct contact with the Sahabah. The tradition then would have been passed from the Tabi‘un to the Tabi‘ al-Tabi‘in, the third link.

The second and third links in the chain of transmission were also of great interest to Muslim scholars, who treated of them in biographical dictionaries and evaluated them for bias and reliability. Sunni and Shia apply different metrics.

Regard for the companions is evident from the hadith:

Narrated Abdullah:
The Prophet said, "The people of my generation are the best, then those who follow them, and then whose who follow the latter.

Sunni Muslim scholars classified companions into many categories, based on a number of criteria. The hadith quoted above shows the rank of ṣaḥābah, tābi‘īn, and tābi‘ at-tābi‘īn.Al-Suyuti recognized eleven levels of companionship. Shia do not have a ranking system dependent on when the Sahabi embraced Islam but according to what they did during their life. If a Sahabah made Muhammad angry or questioned his decision several times then he is viewed as unreliable. Shias consider that any hadith where Muhammad is claimed to have absolved all Sahabah from sin is a false report by those who opposed the Ahl al-Bayt.

The Shia believe that after the death of Muhammad, the majority of the sahabah turned aside from true Islam and deviated from Muhammad's family, instead electing the caliph by themselves at a place called Bani Saqeefa, they did this by a majority vote and elected Abu Bakr as the first caliph. Although some of the sahabah repented later, only a few of the early Muslims held fast to Ali, whom Shia Muslims regard as the rightful successor to Muhammad. Shia scholars therefore deprecate hadith believed to have been transmitted through unjust companions, and place much more reliance on hadith believed to have been related by Muhammad's family members and companions who supported Ali. The Shia believe that Muhammad announced his succession during his lifetime at Dawat Zul Asheera then many times during his prophethood and finally at Ghadeer e Khum.

"Once a male or female Muslim has seen Muhammad only for a short time, no matter whether he/she is a child or an adult, he/she is called a Sahaba with the proviso of dying with as a believer; the same rule applies to blind Muslims who have talked with the Prophet at least once. If a disbeliever sees Muhamma and then joins the Believers after the demise of Muhammad, he is not a Sahaba; nor is a person called a Sahaba if he converted to Islam afterwards although he had seen Muhammad as a Muslim. A person who converts to Islam after being a Sahaba and then becomes a Believer again after the demise of Muhammad, is a Sahaba.

Ibn Sa'd al-Baghdadi, Muhammad – The book of The Major Classes, only partially translated into English; see Men of Medina and Women of Medina published by Ta-Ha Publishers, and first two volumes as published by Kitab Bhavan, New Delhi.